String Formatting

Preparing strings for output

Printing

println(arg) prints its one argument on a line println can be used to print any single value, but it doesn’t work well

with arrays or user-defined data types scala> println(List(1, 2, 3))List(1, 2, 3)

scala> println(Array(1, 2, 3))[I@79916512

When printing a user-defined type, println will first look to see if you have written a toString method that it can use

You can use println without an argument to get a blank line print(arg) works like println, but doesn’t go to the next

line scala> print("abc"); print("xyz")

abcxyz

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Concatenation

The simplest way to print several values at once is to “add” (concatenate) them with a string, with the + operator

When a value is concatenated with a string, the value’s toString method is called

scala> println("Array is " + Array(1, 2, 3) + ", List is " + List(1, 2, 3))Array is [I@3fd87157, List is List(1, 2, 3)

When you study classes, you will learn how to write your own toString methods

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Interpolation

You can insert (interpolate) the value of simple variables into strings by doing two things: Prefix the string with an s Put a $ before the variable name Example: s"Your score is $score"

You can also interpolate the value of expressions by enclosing them in curly braces after the $ Example: s"Twice $x is ${2 * x}"

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Formatting I

Sometimes you want more precise control over the way numbers and dates are printed

Default:scala> println(7 * 0.1)0.7000000000000001

scala> println(new java.util.Date)Sat Jul 20 12:59:33 PDT 2013

Formatted:scala> println("Seven tenths is %5.3f".format(7 * 0.1))Seven tenths is 0.700

scala> println("Today's date is %tD".format(new java.util.Date))Today's date is 07/20/13

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Formatting The syntax is: string.format(value, …, value)

The number and types of values must agree with the format specifiers

Here are examples of the most common format specifiers %12d format an integer right-justified in a field of width 12 %-8d format an integer left-justified in a field of width 8 %5.3f format a floating point number right-justified in a field of width

5, with 3 digits after the decimal point %12.3e like %12.3f, but using scientific (E) notation %7b format a boolean right-justified in a field of width 7 %10s format a string right-justified in a field of width 10

If a field width is too small, will be ignored Irregular spacing is better than printing the wrong number!

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printf

printf(string, value, …, value) is shorthand forprint(string.format(value, …, value))

Note that this is a shorter way to call print, not println

To do the equivalent of a println, put a \n as the last character in the string

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The End